The present invention relates to control of container labeling equipment. More specifically, the invention relates to procedures and apparatus for accurately applying labels, such as pressure sensitive labels, to containers, utilizing continual monitoring of the absolute positions of the container and label in order to correctly apply the labels at high container speeds.
Currently-used label applicator systems frequently use a type of motion control system referred to as xe2x80x9cvelocity slavingxe2x80x9d. Such systems start a predefined move of the label initiated by a stimulus and wherein the velocity of the label is dictated by the ratio-metric velocity of the container. The feedback as to the container velocity is generated by a main container-handling portion of the machine. Additionally, the end point for the application of the labels carried by a carrier web, to a particular container may be advanced or retarded based on a registration stimulus incorporated into the system.
One example of such a system is that which is described in U.S. Pat. No. 4,294,644. In that patent a servomotor is controlled pursuant to input of information relating to the relative velocities of the container and labels. One important limitation of such systems relates to the inability of many such systems to accelerate the velocity of a web carrying the labels to the linear velocity of the containers. This problem is particularly acute with respect to short labels.
In the ""644 patent there is described a control system for a servomotor which is responsive to the rate of feed or speed of the surface to be labeled as it is advanced to the labeler. One aspect of this previous system is to bring the servomotor up to a determined speed which is then held constant based on a assumption that conveyor speed is constant, so that the pulse output derived from a servomotor encoder will match the pulse output derived from the conveyor encoder. Such control systems are an essential feature of speed matching, i.e., xe2x80x9cvelocity slavingxe2x80x9d.
Another significant limitation of the velocity slaved labeling process is due to the fact that it is linear in nature. Such linearity is manifested by the direct speed match between the master encoder and predictable linear acceleration and deceleration ramps controlling movement of the labels. By utilizing the linear properties of the velocity profile, basically a trapezoid, the label placement position is derived. Such devices are limited by the fact that very complex requirements may be needed to match the label velocity to the container surface velocity but the master encoder still runs at a constant rate thereby ruling out complex moves. One situation where such applicators fail is where the length of the material available to accelerate to the surface velocity of the container is too short. In this condition there is a requirement that the label carrier web must first be backed up before acceleration begins, which backup move would be a low acceleration, deceleration move in order to maintain necessary web tension, but a simple velocity slaved servo system cannot perform such a function. Limitations are also caused due to unusual shapes of some containers or due to unusual geometry of the labels which may require complex move profiles, which velocity slaved system cannot perform.
It is a principal object of the present invention to provide a new labeling control system which overcomes the foregoing limitations by utilizing a position slaved motion control system. An important aspect of the present invention is to provide a position slaved system which incorporates sufficient mathematical power to generate the necessary move profiles to control high speed labeling equipment. Such mathematical power is provided by the provision of high speed microprocessors used in conjunction with appropriate mathematical algorithms.
A further important aspect of the present invention involves the intimate coupling of the slave motion control system, which controls a label carrier web""s position, to the position of the master feedback device, i.e., an encoder or a resolver, and thus to the position of the containers. In accordance with this aspect, an ability to offset the commanded position of the container (or other specific object on a container) is provided. This offset, in the form of an electronic signal received from a sensing device, identifies the absolute location of the container or object such as a previously applied label, which, in effect, produces an absolute position independent of the main container handling portion of the machine but which is relative to each container or object on the container. Further, in accordance with this aspect, a high precision position control results in the ability to provide very complex motion even at speeds of 750 labels per minute. Further, in accordance with this aspect, the motion of the label-carrying web is not linear with respect to the position of the master, i.e., the container handler. Further, even though accurate label placement cannot be predicted by means of velocity in complex non-linear situations, the use of position slaving, in accordance with the invention, overcomes this limitation.
In accordance with a further aspect of the invention a mathematical algorithm is provided for each specific container configuration or shape to allow for the ability to generate complex move profiles. In connection with such algorithms the position of the label carrier web is related mathematically to the position of each container as it travels and possibly rotates past the label application head. In a general sense the position of the slave carrier web is a function of the position of the master as follows:
Slave_position=f(master_position)
The function of the slave web position must be continuous throughout all master-feedback positions. Therefore, in the case of multiple functions, the first derivative of each function at the endpoint must equal the first derivative of the next function at its start point. That is, for successive functions ƒ1(i) and ƒ2(i), where i0 less than i less than iƒ and iƒ less than i less than jƒ respectively for functions ƒ1(i) and ƒ2(i) we have:
dƒ1(iƒ)/di=dƒ2(iƒ)/di
This is adhered to so that a step change in velocity does not occur which could be detrimental to the label placement and damaging to the web material.
Briefly, the invention provides a method of labeling containers which includes providing a container handling machine such as conveyor in the case of an inline labeling machine, and a rotary bottle table in the case of a rotary labeling machine, for successively transporting containers past a label application station. The container handling machine i.e., xe2x80x9cmachine basexe2x80x9d has an associated position signaling device such as a rotary encoder for providing data in electronic form identifying the position of the machine. In the preferred embodiment the encoder makes one revolution each time the container handling machine translates a distance equal to the center-to center distance between successive containers. As will be appreciated by those skilled in the are, the encoder could be set to make more than one revolution per machine pitch, if desired.
A label applicator is driven by a servomotor with said servomotor being controlled by a microprocessor-based slave position motion controller. The label applicator includes an electronic signal generator identifying the motion controller position of each successive label dispensed by the label applicator.
A machine base position control or identifying microprocessor is operatively connected to the label applicator""s motion controlling microprocessor and to the machine base encoder. An electronic signal generator identifying the physical position of the container or object such as a previously applied label on the container surface is operatively connected to the position control microprocessor. The machine base position control microprocessor generates signals to the label applicator""s motion controlling microprocessor that relates the position of the container to be labeled.
The label applicator servomotor contains an associated position identifying device such as an encoder that provides electronic data to the motion control microprocessor that relates to servo motor position and velocity. The motion control microprocessor is operatively connected to a label applicator servo amplifier, the servo motor encoder and to the machine base encoder. The label applicator servo amplifier is operatively connected and provides power to the label applicator servomotor. The motion control microprocessor generates a move profile for each successive label, using mathematical algorithms, and electronically controls the label applicator servo amplifier to vary the torque applied by the servomotor. Electronic feedback signals from the servo motor encoder and machine encoder to the motion control microprocessor provide the electronic position and velocity feedback data needed to control the torque applied by the servo amplifier and servo motor. Typically in accordance with the invention, such signals are continually generated and processed at a rate of at least once each 125th microsecond.
In accordance with a further aspect of the invention, a host microprocessor generates a pitch based electronic shift register that contains information on the labeling processes that need to be performed on a container. The host microprocessor provides the labeling commands and is operatively connected to a label position motion control microprocessor.